1. Field of the Invention
The present invention relates to a heat treatment apparatus, more specifically to a technique that improves accuracy of temperature measurement of the object to be processed, such as a semiconductor wafer.
2. Description of the Related Art
The semiconductor device manufacturing process employs several sorts of heat treatment apparatuses that perform heat treatments, such as oxidation, diffusion, and film-forming. A batch-type, vertical-type heat treatment apparatus, which performs a heat treatment to a plurality of objects at one time, is known as one of the aforementioned heat treatment apparatuses.
With the batch-type, vertical-type heat treatment apparatus, a plurality of semiconductor wafers are held by a wafer boat vertically spaced at intervals, and then the wafer boat is loaded into the processing vessel. The semiconductor wafers are heated up to a predetermined temperature by means of a tubular heater surrounding the processing vessel, and then the semiconductor wafers are subjected to a predetermined treatment. A temperature controller controls the output power of the heater based on the temperature data measured by a temperature sensor unit arranged in the processing vessel, thereby the interior of the processing vessel, and thus the semiconductor wafers, is maintained at a predetermined temperature.
In order to obtain films having excellent property and uniform quality, uniform temperature distribution on each semiconductor wafer and between semiconductor wafers respectively placed at different heights is necessary. Thus, the interior of the processing vessel is divided into a plurality of heating zones, and the output power of each heater corresponding to each heating zone is independently controlled.
The temperature sensor unit used in such heat treatment apparatus is composed of: a straight protective tube made of quartz and extending vertically in the processing vessel; and thermocouples arranged in the protective tube at positions respectively corresponding to the heating zones. The thermocouples measure temperatures at positions in the processing vessel respectively corresponding to the heating zones, and the calorific power of the heaters is controlled based on the measured temperatures.
FIG. 6 shows a typical structure of a conventional temperature sensor unit. A thermocouple 60 is made by connecting a metallic wire 61A of platinum and a metallic wire 61B of platinum-rhodium alloy. The metallic wires 61A and 61B are inserted into tubular, electrically insulative members 62A and 62B, which are made of alumina ceramics. The metallic wires 61A and 61B extend within a protective tube 65 made of quartz, are drawn outside the end part of the protective tube 65, and are connected to a controller.
However, the transient response of the above temperature sensor unit is slow in view of the temperature rising rate of the semiconductor wafer, when they are being heated rapidly. If the rising of the temperature measured by thermocouple is slower than the rising of the actual temperature of the semiconductor wafer when the semiconductor wafer is heated, accurate temperature control is difficult, and thus a long time period is required for the semiconductor wafers to reach a stable condition in which they are at the predetermined process temperature. This lengthens the total processing time, resulting in reduction in throughput.